Run closed_world2_test using the normal compiler pipeline.

tests/compiler/dart2js/compiler_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import "dart:async";
 
 import "package:async_helper/async_helper.dart";
 import 'package:compiler/compiler.dart';
 import "package:compiler/src/elements/elements.dart";
 import "package:compiler/src/old_to_new_api.dart";
 import "package:expect/expect.dart";
 
 import "mock_compiler.dart";
 
 Future testErrorHandling() {
   // Test that compiler.currentElement is set correctly when
   // reporting errors/warnings.
   MockCompiler compiler = new MockCompiler.internal();
   return compiler.init().then((_) {
     compiler.parseScript('NoSuchPrefix.NoSuchType foo() {}');
-    FunctionElement foo = compiler.mainApp.find('foo');
+    LibraryElement mainApp = compiler.mainApp;
+    FunctionElement foo = mainApp.find('foo');
     compiler.diagnosticHandler = new LegacyCompilerDiagnostics(
         (Uri uri, int begin, int end, String message, Diagnostic kind) {
       if (kind == Diagnostic.WARNING) {
         Expect.equals(foo, compiler.currentElement);
       }
     });
     foo.computeType(compiler.resolution);
     Expect.equals(1, compiler.diagnosticCollector.warnings.length);
   });
 }
 
 main() {
   asyncTest(() => testErrorHandling());
 }